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| United States Patent |
5,656,407
|
|
Kawahara
|
August 12, 1997
|
Photosensitive material for electrophotography
Abstract
A photosensitive material for electrophotography, wherein the
charge-generating agent comprises a P-type charge-generating pigment and
an N-type charge-generating pigment in combination, at least part of these
pigments being present in the form of aggregates in the photosensitive
layer. The photosensitive material will assume the form of either a single
dispersion type or a laminated layer type, and exhibits very high carrier
generation efficiency, strikingly improved sensitivity on the side of long
wavelengths, excellent balance in the spectral sensitivity and property
after repetitively used, and can hence be effectively used for forming
image by the electrophotography.
| Inventors:
|
Kawahara; Akihiko (Osaka, JP)
|
| Assignee:
|
Mita Industrial Co., Ltd. (Osaka, JP)
|
| Appl. No.:
|
266503 |
| Filed:
|
June 27, 1994 |
Foreign Application Priority Data
| Jun 29, 1993[JP] | 5-159700 |
| Mar 23, 1994[JP] | 6-051522 |
| Current U.S. Class: |
430/78; 430/56; 430/83; 430/91; 430/95; 430/133; 430/134 |
| Intern'l Class: |
G03G 005/09 |
| Field of Search: |
430/83,78,133,134,59,56,91,95
|
References Cited
U.S. Patent Documents
| 3992205 | Nov., 1976 | Wiedemann.
| |
| 4855202 | Aug., 1989 | Yoshihara et al. | 430/59.
|
| 4877702 | Oct., 1989 | Miyamoto et al. | 430/72.
|
| 4882254 | Nov., 1989 | Loutfy et al. | 430/83.
|
| 4983483 | Jan., 1991 | Tsai | 430/59.
|
| 5063126 | Nov., 1991 | Nakatani et al. | 430/59.
|
| 5153088 | Oct., 1992 | Muto et al. | 430/78.
|
| Foreign Patent Documents |
| 0385440 | Sep., 1990 | EP.
| |
| 0470729 | Feb., 1992 | EP.
| |
| 0491316 | Jun., 1992 | EP.
| |
| 2249367 | May., 1975 | FR.
| |
| 59-116753 | Jul., 1984 | JP | 430/78.
|
| 63-18353 | Jan., 1988 | JP | 430/78.
|
| 5-232724 | Sep., 1993 | JP | 430/78.
|
| 5-333575 | Dec., 1993 | JP.
| |
| 2231166 | Nov., 1990 | GB.
| |
Other References
Patent & Trademark English Language Translation of JP 5-333575 (Pub Dec.
1993).
Database WPI, Derwent Publications Ltd., London, GB, AN-128841(04). of
Japanese Patent 05-333575 (Pub Dec. 17, 1993).
|
Primary Examiner: Dote; Janis L.
Attorney, Agent or Firm: Sherman and Shalloway
Claims
I claim:
1. A photosensitive material for electrophotography having an electrically
conducting substrate and a photosensitive layer containing a
charge-generating agent and a charge-transporting agent, wherein said
charge-generating agent comprises (A) grains of P-type charge-generating
pigment selected from the group consisting of X-type metal-free
phthalocyanine, oxotitanyl phthalocyanine and metal-free naphthalocyanine
and (B) grains of N-type charge-generating pigment; wherein the grains of
P-type charge-generating pigment and the grains of N-type
charge-generating pigment are present, at a ratio by weight, in the range
of from 10:0.1 to 0.1:10, and wherein said grains of P-type and said
grains of N-type are pretreated together by a wet method or a dry method
and dispersed in a binder whereby the charge-generating agent forms
aggregates comprised of a plurality of grains of said P-type
charge-generating pigment aggregated via a plurality of grains of said
N-type charge-generating pigment.
2. The photosensitive material of claim 1 wherein the weight ratio of said
P-type grains to said N-type grains is in the range of from 10:0.5 to
0.5:10.
3. A photosensitive material for electrophotography having an electrically
conducting substrate and a photosensitive layer containing a
charge-generating agent and a charge-transporting agent, wherein said
charge-generating agent comprises (A) grains of P-type charge-generating
pigment selected from the group consisting of X-type metal-free
phthalocyanine, oxotitanyl phthalocyanine and metal-free naphthalocyanine
and (B) grains of N-type charge generating agent selected from the group
consisting of N-type inorganic semiconductor and N-type inorganic
photoconductor wherein the grains of P-type charge-generating pigment and
the grains of N-type charge-generating agent are present, at a ratio by
weight, in the range from 10:1 to 1:40, and wherein said grains of P-type
and said grains of N-type are pretreated together by a wet method or a dry
method and dispersed in a binder whereby the charge-generating agent forms
aggregates comprised of a plurality of grains of said P-type
charge-generating pigment aggregated via a plurality of grains of said
N-type charge-generating agent.
4. The photosensitive material of claim 3 wherein the weight ratio of the
P-type grains to the N-type grains is in the range of from 2:1 to 6:40.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photosensitive material for
electrophotography and, more specifically, to a sensitized photosensitive
material for electrophotography.
2. Description of the Prior Art
Widely used photosensitive materials for electrophotography can be
represented by those of the function separated-type that are obtained by
providing on an electrically conducting substrate a photosensitive layer
which contains a charge-generating agent and a charge-transporting agent.
The photosensitive materials of this type can roughly be divided into
those of the type of a so-called single dispersion layer obtained by
dispersing a charge-generating agent in a medium that contains a
charge-transporting agent and those of the type of a so-called laminated
layer obtained by providing on the electrically conducting substrate, the
charge-generating agent and the charge-transporting layer in the order
mentioned or in a reverse order.
As the charge-generating agent, there are used, in many cases, P-type
charge-generating pigments such as phthalocyanine pigment and like pigment
as well as N-type charge-generating pigments such as perylene pigment, azo
pigment and like pigment. Generally, however, these pigments have poor
balance in the spectral sensitivity. When use is made only of the N-type
charge-generating pigment such as perylene pigment or azo pigment, in
particular, sensitivity is low on the side of long wavelengths of from 600
to 700 nm and fogging occurs on a yellow-base paper. In designing a
photosensitive material that can be used in common for the halogen source
of light, fluorescent source of light and laser source of light, it is
desired that the photosensitive material has panchromatic spectral
sensitivity. There is, however, available no pigment that meets the above
requirement, and technology has been proposed for using plural kinds of
pigments as described below.
Japanese Laid-Open Patent Publication No. 222961/1990 filed by the present
applicant discloses a photosensitive material of the laminated layer type
in which a charge-transporting layer and a charge-generating layer are
provided on an electrically conducting substrate in the order mentioned,
by using, as charge-generating agents, an N-type pigment
(dibromoanthanthrone) and a P-type pigment (metal-free phthalocyanine) at
a ratio of from 40/80 to 90/10.
Moreover, Japanese Laid-Open Patent Publication No. 228670/1990 discloses
the use of an X-type metal-free phthalocyanine in an amount of from 1.25
to 3.75 parts by weight in combination per 100 parts by weight of a
perylene pigment.
In the case of the former proposal (Japanese Laid-Open Patent Publication
No. 222961/1990) using the N-type pigment and the P-type pigment in
combination, when the photosensitive material is positively charged by the
corona discharge, an electric field established by the corona discharge
acts upon the P-type pigment that is electrically in a neutral state,
whereby thermal holes are injected into the charge-transporting layer from
the P-type pigment to neutralize the negative electric charge induced on
the side of the substrate. Besides, negative space charge exists in the
charge-generating layer which is the outermost layer, and intensifies the
electric field together with the positive charge on the surface of the
photosensitive material to enhance the photocarrier generation efficiency.
However, this effect is obtained only when the charge-transporting layer
and the charge-generating layer are provided in this order on the
electrically conducting substrate, which is not still satisfactory from
the standpoint of improving the photocarrier generation efficiency.
According to the above latter proposal (Japanese Laid-Open Patent
Publication No. 228670/1990) which uses the N-type pigment and the P-type
pigment in combination, the sensitivity to red light is improved to some
extent. However, this photosensitive material in which the N-type pigment
(X-type metal-free phthalocyanine) is added to the P-type pigment
(perylene pigment) which is a main pigment, so that these pigments are
simply dispersed together in a binder resin, is not still satisfactory
from the standpoint of improving the photocarrier generation efficiency
and is not still satisfactory, either, for being used in such applications
as in a high-speed laser printer and the like.
SUMMARY OF THE INVENTION
The present inventors have attempted to use a P-type charge-generating
agent and an N-type charge-generating agent or an N-type inorganic
semiconductor or photoconductor as a charge-generating agent, at least
part of the charge-generating agent being contained in the form of
aggregates in the photosensitive layer, and have obtained markedly
improved carrier generation efficiency as compared with when the P-type
charge-generating agent and the N-type charge-generating agent are simply
dispersed together. In this case, the present inventors have further
discovered the facts that the sensitivity is strikingly improved on side
of long wavelengths, the photosensitive layer exhibits excellent balance
in the spectral sensitivity and that the photosensitive layer exhibits
improved abrasion resistance.
That is, the object of the present invention is to provide a photosensitive
material for electrophotography containing a charge-generating agent and a
charge-transporting agent, which exhibits markedly improved carrier
generation efficiency, strikingly improved sensitivity on the side of long
wavelengths, excellent balance in the spectral sensitivity and excellent
properties even after used repetitively.
According to the present invention, there is provided a photosensitive
material for electrophotography having an electrically conducting
substrate and a photosensitive layer containing a charge-generating agent
and a charge-transporting agent, wherein said charge-generating agent
comprises a P-type charge-generating pigment and an N-type
charge-generating pigment or an N-type inorganic semiconductor or
photoconductor, and at least part of said charge-generating agent is
dispersed in the form of aggregates in the photosensitive, layer.
The aggregates of the charge-generating agent present in the photosensitive
layer of the present invention have aggregated structure in which a plural
number of grains of the P-type charge-generating pigment (hereinafter
often called P-type charge-generating grains) or a plural number of grains
of the N-type charge-generating pigment or the N-type inorganic
semiconductor or photoconductor (hereinafter often called N-type
charge-generating grains) are aggregated together via the N-type
charge-generating grains or the P-type charge-generating grains. The
aggregates should generally have a grain size of from 0.2 to 2 .mu.m.
Presence of aggregates and aggregated structure in the photosensitive layer
of the present invention can be confirmed relying both upon a
transmission-type electron microphotography and an energy dispersion-type
X-ray spectral method. In this specification, the grain size is defined as
a one-half value of the sum of a long diameter of a grain and a short
diameter of a grain.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sketch from a transmission-type electron microphotography of a
photosensitive layer of the present invention;
FIG. 2 is a sketch from a transmission-type electron microphotography of a
conventional photosensitive layer of the type in which the agents are
dispersed together;
FIG. 3 is a sectional view of a photosensitive material of the type of
single dispersion layer for electrophotography;
FIG. 4 is a sectional view of a photosensitive material of the laminated
layer type for electrophotography; and
FIG. 5 is a sectional view of another photosensitive material of the
laminated layer type for electrophotography.
DETAILED DESCRIPTION OF THE INVENTION
In the accompanying drawings, FIG. 1 is a sketch from a transmission-type
electron microphotography of a photosensitive layer of the present
invention and FIG. 2 is a sketch from the transmission-type electron
microphotography of a conventional photosensitive layer in which the
agents are dispersed together. In these drawings, hatched grains are
P-type charge-generating grains, and dotted grains are N-type
charge-generating grains.
It will be obvious from these drawings that in the conventional
photosensitive layer, the P-type charge-generating pigment and the N-type
charge-generating pigment are dispersed in the form of individual grains
in a resin medium (continuous phase) whereas in the photosensitive layer
of the present invention, the P-type charge-generating grains and the
N-type charge-generating grains are aggregated constituting an aggregated
structure in which a plural number of the P-type (N-type)
charge-generating grains are aggregated together via N-type (P-type)
charge-generating grains, and in which aggregates of the grains are
growing. In a concrete example shown in FIG. 1, furthermore, it will be
understood that part of the N-type charge-generating grains contained in a
large amount exist in the form of a dispersion of individual grains in
addition to being aggregated but the P-type charge-generating grains which
are contained in a small amount exist mostly in the form of aggregates.
According to the present invention as described above, the P-type
charge-generating grains and the N-type charge-generating grains at least
partly assume the form of aggregates exhibiting markedly improved carrier
generation efficiency and giving advantages in regard to increased
sensitivity on the side of long wavelengths, improved balance in the
spectral sensitivity of the photosensitive layer, and enhanced durability
of the photosensitive layer.
Reference should be made to Examples appearing later. When, for example, an
N-type charge-generating pigment (perylene) is used alone (Comparative
Example 1), fairly good sensitivity is obtained on the side of relatively
short wavelengths (500 nm) but almost no sensitivity is obtained on the
side of long wavelengths (700 nm). When a P-type charge-generating pigment
(phthalocyanine) is used alone (Comparative Examples 2 and 3), on the
other hand, fairly good sensitivity is obtained on the side of relatively
long wavelengths but almost no sensitivity is obtained on the side of
relatively short wavelengths, both of which give poor balance in the
spectral sensitivity.
By giving attention to the sensitivity, furthermore, even when the P-type
charge-generating grains and the N-type charge-generating grains are used
in combination, the system in which these grains are individually
dispersed together (Comparative Example 4) gives a result which is nothing
but the combination of the result of when the N-type charge-generating
grains (perylene) were used alone (Comparative Example 1) and the result
of when the P-type charge-generating grains (phthalocyanine) were used
alone (Comparative Example 2). Thus, no improvement is recognized in the
carrier generation efficiency, and the sensitivity becomes poor
particularly on the side of long wavelengths and the surface potentials
(both the initial potential and the residual potential after exposure to
light) vary greatly after being used repetitively.
On the other hand, when aggregates of the P-type charge-generating grains
and the N-type charge-generating grains are formed in advance according to
the present invention and are made present in the photosensitive layer
(Example 1), the photosensitive layer exhibits improved balance in the
spectral sensitivity at every wavelength and exhibits markedly improved
sensitivity on the side of long wavelengths despite the P-type
charge-generating grains and the N-type charge-generating grains are
blended in the photosensitive layer at the same ratio as that of
Comparative Example 4. This is considered to stem from an increased
carrier generation efficiency. Moreover, the surface potentials vary
within suppressed small ranges even after being used repetitively.
Moreover, the sensitivity (700 nm) of nearly an equal level is obtained
when the P-type charge-generating grains (phthalocyanine) and the N-type
charge-generating grains (perylene) are used in combination at a ratio of
3 parts by weight and 10 parts by weight to form aggregates in advance,
which are then made present in the photosensitive layer (Example 5) and
when the P-type charge-generating grains (phthalocyanine) are used alone
in an amount of 10 parts by weight (Comparative Example 3). This is
because in Example 5 where the aggregates are formed, the N-type
charge-generating grains that are added in an amount of even 3 parts by
weight help improve the carrier generation efficiency owing to microscopic
P-N junctions, making it possible to exhibit the effect comparable to that
of when the N-type charge-generating grains (phthalocyanine) are used
alone in an amount of 10 parts by weight.
By using the structure in which the agents are dispersed together,
furthermore, the sensitivity (500 nm and 700 nm) comparable to that of the
structure in which aggregates are present in the photosensitive layer is
obtained only by increasing the amount of the P-type charge-generating
grains (Comparative Example 8). In this case, however, surface potentials
(initial potential and residual potential after exposure to light) vary
greatly after being used repetitively.
The above-mentioned improvement in the photosensitive layer of the present
invention was found as phenomenon by the present inventors through
extensive study. According to the present inventors, the improvement is
obtained presumably because of the following reasons.
In the photosensitive layer of the present invention, the P-type
charge-generating grains or the N-type charge-generating grains establish
aggregated structure in which they are aggregated via grains of the
opposite polarity, and in the aggregated grains are formed numerous P-N
Junctions on the interfaces among the primary grains. In the
photosensitive layer of the present invention, it is believed that the
carrier generation efficiency is improved in a broad wavelength zone
inclusive of the long wavelength region owing to the formation of PN
junctions, contributing to increasing the sensitivity.
Furthermore, the photosensitive material of the present invention can be
electrically charged into either polarity, and electrostatic latent image
can be formed on the surface of the photosensitive layer either when it is
positively charged or negatively charged. This is presumably because the
sensitivity is obtained with either polarity owing to
electron-transporting property of the N-type charge-generating grains and
hole-transporting property of the P-type charge-generating grains.
When the N-type inorganic semiconductor or photoconductor is used as the
N-type charge-generating grains in accordance with the present invention,
furthermore, the aforementioned aggregated structure is formed and,
besides, the grains exhibit a large hardness presenting another advantage
in that the photosensitive layer as a whole is effectively prevented from
being worn out.
Photosensitive Material
In the photosensitive material of the present invention, the photosensitive
layer may contain the charge-generating agent and the charge-transporting
agent either in the form of laminated layers or a single layer dispersion.
Here, however, the single layer dispersion helps most distinctly exhibit
the effect for forming microscopic P-N junctions on the interfaces among
the primary grains since the pigment concentration is low in the layer.
With reference to FIG. 3, the photosensitive material for
electrophotography comprises an electrically conducting substrate 1 on
which a single photosensitive layer 2 is provided containing the
charge-generating agent and the charge-transporting agent therein. The
layer 2 of generating and transporting the electric charge comprises a
composition of a continuous phase which contains the charge-transporting
agent (CTM) and a dispersion phase of a particular charge-generating agent
(CGM) that is dispersed in the continuous phase as will be described later
in detail.
With reference to FIG. 4, another photosensitive material for
electrophotography comprises an electrically conducting substrate 1 on
which are provided a charge-generating layer (CGL) 3 containing a
particular charge-generating agent that will be described below in detail
and a charge-transporting layer (CTL) 4 in the order mentioned.
With reference to FIG. 5, a further photosensitive material for
electrophotography comprises an electrically conducting substrate 1 on
which are provided a charge-transporting layer (CTL) 5 and a
charge-generating layer (CGL) 6 containing a particular charge-generating
agent that will be mentioned below in detail in the order mentioned.
In these photosensitive materials, the photosensitive layer 2, the
charge-transporting layer 4 or the charge-transporting agent (CTM) in the
layer 5 may comprise a positive hole-transporting agent, an
electron-transporting agent, or a combination thereof.
Though not diagramed in FIGS. 3 to 5, the photosensitive material of the
present invention may be provided, as an uppermost layer, with a
protection layer that has been known per se, such as the one which
contains, for example, a charge-transporting agent/or the electrically
conducting fine powder.
Charge-Generating Agent
According to the present invention, the P-type charge-generating grains and
the N-type charge-generating grains are used in combination as a
charge-generating agent, and at least part of them are made present in the
form of aggregates in the photosensitive layer.
Each aggregate comprises a plurality of the P-type (or the N-type)
charge-generating grains which are aggregated together via the N-type (or
the P-type) charge-generating grains of the contrasting polarity, and
numerous P-N junctions exist in the aggregates.
As the P-type charge-generating grains constituting the aggregates of the
present invention, there can be used a known P-type charge-generating
pigment such as phthalocyanine pigment, naphthalocyanine pigment and other
porphyrin pigments.
The porphyrin pigments have a skeleton represented by the following formula
(1),
##STR1##
wherein Z is a nitrogen atom or a CH group, R1 and R2 are substituted or
unsubstituted monovalent hydrocarbon groups having not more than 12 carbon
atoms, and R1 and R2 being coupled together may form a substituted or
unsubstituted benzene ring or naphthalene ring together with carbon atoms
bonded thereto.
Particularly preferred examples include:
X-type metal-free phthalocyanine,
oxotitanyl phthalocyanine, and
metal-free naphthalocyanine.
It is desired that the P-type charge-generating pigment usually has a grain
size of from 0.1 to 1 .mu.m.
As the N-type charge-generating grains that constitute aggregates, there
can be used a known N-type charge-generating pigment such as perylene
pigment, azo pigment, squarylium pigment or polycyclic quinone pigment.
There can be further used an N-type semiconductor or photoconductor in
addition to the above.
The perylene pigment will have the following formula (2),
##STR2##
wherein R3 and R4 are each a substituted or unsubstituted alkyl group with
not more than 18 carbon atoms, a cycloalkyl group, an aryl group, or an
aralkyl group,
and the substituent may be an alkoxy group, a halogen atom or the like.
As the azo pigment, any charge-generating pigment that has heretofore been
used can be used such as monoazo pigment, disazo pigment or trisazo
pigment.
The squarylium pigment will have the following formula
##STR3##
wherein R5 and R6 are each an alkyl group, an alkoxy group, or a halogen
atom, R7, R8, R9 and R10 are each an alkyl group, a cycloalkyl group, an
alkoxy group, a halogen atom, an aryl group, or an aralkyl group, and each
of the groups may have an alkyl group, an alkoxy group or a halogen atom
as a substituent.
As the polycyclic quinone pigment, there can be used anthanthrone pigment,
quinacridone pigment, perynone pigment, quinophthalone pigment,
flavanthrone pigment, pyranthrone pigment, violanthrone pigment, anthrone
pigment or indanthrone pigment.
It is desired that the above-mentioned N-type charge-generating pigment
usually has a primary grain size of from 0.1 to 1 .mu.m. The P-type
charge-generating pigment and the N-type charge-generating pigment should
be used in amounts providing a weight of from 10:0.1 to 0.1:10 and,
particularly, from 10:0.5 to 0.5:10.
As the N-type inorganic semiconductor or photoconductor, there is usually
used a semiconductor or a photoconductor of the type of an inorganic
oxide. Preferred examples include, titanium oxide (TiO.sub.2), tin oxide
(SnO.sub.2), indium-doped tin oxide (ITO), antimony-doped tin oxide and
zinc oxide (ZnO).
The inorganic semiconductor or photoconductor should usually be in a fine
particular form having a primary grain size of from 0.01 to 5 .mu.m and,
particularly, from 0.1 to 1 .mu.m.
From the standpoint of sensitivity, there exists an optimum range in the
ratio of blending the P-type organic charge-generating pigment (A) and the
N-type inorganic semiconductor or photoconductor (B). In general, the
weight ratio A:B should be from 10:1 to 1:40 and, particularly, from 2:1
to 8:40. When the ratio of the inorganic semiconductor or photoconductor
is greater than the above range, the charging property of the
photosensitive layer tends to decrease. When the ratio thereof is smaller
than the above range, on the other hand, the sensitivity is not much
improved and the abrasion resistance is not sufficiently improved, either.
Formation of Aggregates
According to the present invention, aggregates of the P-type
charge-generating grains and the N-type charge-generating grains are not
formed by simply dispersing them together in a resin solution, and a
pretreatment must be carried out.
The pretreatment can be by either a wet method or a dry method. In the wet
method, the P-type charge-generating grains and the N-type
charge-generating grains are dispersed in a finely pulverized form in a
particular polar solvent such as a tetrahydrofuran or a dichloromethane to
form aggregates thereof.
In these solvents, the two grains are finely pulverized and are dispersed,
so that the P-type charge-generating grains are positively charged and the
N-type charge-generating grains are negatively charged to effectively form
aggregates.
The present inventors have confirmed through experiments the fact that even
when the grains are mixed together in an organic solvent, the individual
grains are not stably dispersed and the efficiency for forming aggregates
strikingly decreases when there is used an alcohol, cyclohexane, toluene
or dioxane.
In the wet method, the aggregates can be effectively formed by effecting
the wet pulverization using a ball mill, a colloid mill, a disperse mill
or a homo mixer.
In the dry method, the P-type charge-generating grains and the N-type
charge-generating grains are mixed together and are pulverized together.
Even by the mechano-chemical method, the grains are ground into primary
grains which then aggregate together, so that aggregates grow. In the dry
method, the pulverization is carried out using a ball mill and a vibration
mill together.
The P-type charge-generating grains and the N-type charge-generating grains
can be used in amounts of the above-mentioned ratio. In the case of the
photosensitive material of the positively charged type, the photosensitive
material should advantageously be comprised chiefly of the N-type
charge-generating grains. By forming the aggregates by blending the P-type
charge-generating grains in small amounts, improved balance is obtained in
the spectral sensitivity and the sensitivity can be increased on the side
of long wavelengths.
In the case of the photosensitive material of the negatively charged type,
the photosensitive material should advantageously be comprised chiefly of
the P-type charge-generating grains. By forming the aggregates by blending
the N-type charge-generating grains in small amounts, improved balance is
obtained in the spectral sensitivity and the sensitivity can be increased
on the side of long wavelengths.
By using the P-type charge-generating grains and the N-type
charge-generating grains at a nearly equal ratio, furthermore, there is
obtained a photosensitive material of the type that can be charged into
either polarity.
When the ratio of the amounts of the P-type charge-generating grains and of
the N-type charge-generating grains is deviated to either side, the grains
of the side of the larger amount may exist in the form of individual
grains liberated from the aggregates. However, the presence of such free
grains does not adversely affect the sensitivity.
The aggregates used in the present invention are made up of a plurality of
the P-type (N-type) charge-generating grains that are aggregated together
via the N-type (P-type) charge-generating grains, and should have a grain
size of from 0.2 to 2 .mu.m.
When the grain size exceeds 2 .mu.m, the sensitivity and electrically
charging performance of the photosensitive material tend to decrease. This
is attributed to that the central grains in the aggregates are concealed
and that the light-receiving areas decrease. It is further considered that
the presence of giant grains permits the electric charge to leak in the
photosensitive layer, which causes the electrically charging performance
to decrease.
When the grain size of the aggregates is smaller than the above-mentioned
range, on the other hand, balance in the spectral sensitivity decreases
compared with that of when the grain size lies within the above-mentioned
range, and the sensitivity decreases on the side of long wavelengths.
Photosensitive Material of the Single Layer Type
In the photosensitive material of the single layer type, aggregates of the
P-type and N-type charge-generating grains and the charge-transporting
agent are dispersed in a solution of a binder resin for forming the
photosensitive layer, and this coating composition is provided on the
electrically conducting substrate to obtain a single-layer photosensitive
material.
The coating solution is prepared by a known method using, for example, a
roll mill, a ball mill, an attritor, a paint shaker or an ultrasonic
dispersing machine, and is then applied using a widely known coating
means, followed by drying.
As the charge-transporting agent, there can be used any known
electron-transporting agent or positive hole-transporting agent, such as
the compounds exemplified below. These charge-transporting agents can be
used in a single kind of in a combination of a plurality of kinds. For
instance, the electron-transporting agent can be used in combination with
a small amount of the positive hole-transporting agent or, conversely, the
positive hole-transporting agent can be used in combination with a small
amount of the electron-transporting agent.
Preferred examples of the electron-transporting agent include:
2,6-dimethyl-2',6'-di-t-butyldiphenoquinone,
2,2'-dimethyl-6,6'-di-t-butyldiphenoquinone,
2,6'-dimethyl-2',6-di-t-butyldiphenoquinone,
2,6,2',6'-tetramethyldiphenoquinone,
2,6,2',6'-tetra-t-butyldiphenoquinone,
2,6,2',6'-tetraphenyldiphenoquinone,
2,6,2',6'-tetracyclohexyldiphenoquinone,
chloroanil,
bromoanil,
tetracyanoethylene,
tetracyanoquinodimethane,
2,4,7-trinitro-9-fluorenone,
2,4,5,7-tetranitro-9-fluorenone,
2,4,7-trinitro-9-dicyanomethylene fluorenone,
2,4,5,7-tetranitroxanthone, and
2,4,8-trinitrothioxanthone.
Preferred examples of the positive hole-transporting agent include:
N-ethylcarbazole,
N-isopropylcarbazole,
N-methyl-N-phenylhydrazino-3-methylidyne-9-carbazole,
N,N-diphenylhydrazino-3-methylidyne-9-thylcarbozole,
N,N-diphenylhydrazino-3-methylidyne-10-ethylphenothiazine,
N,N-diphenylhydrazino-3-methylidyne-10-ethylphenoxazine,
p-diethylaminobenzaldehyde-N,N-diphenylhydrazone,
p-diethylaminobenzaldehyde-.alpha.-naphthyl-N-phenylhydrazone,
p-pyrrolydinobenzaldehyde-N,N-diphenylhydrazone,
1,3,3-trimetylindolenine-.omega.-aldehyde-N,N-diphenylhydrazone,
p-diethylbenzaldehyde-3-methylbenzthiazolinone-2-hydrazone,
2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole,
1-phenyl-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,
1-[quinonyl(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline
1-[pyridyl(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,
1-[6-methoxypyridyl(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)py
razoline,
1-[pyridyl(3)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,
1-[lepidyl(3)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,
1-[pyridyl(2)]-3-(p-diethylaminostyryl)-4-methyl-5-(p-diethylaminophenyl)py
razoline,
1-[pyridyl(2)]-3-(.alpha.-methyl-p-diethylaminostyryl)-3-(p-diethylaminophe
nyl)pyrazoline,
1-phenyl-3-(p-diethylaminostyryl)-4-methyl-5-(p-diethylaminophenyl)pyrazoli
ne,
2-(p-diethylaminostyryl)-3-diethylaminobenzoxazole,
2-(p-diethylaminophenyl)-4-(p-dimethylaminophenyl)-5-(2-chlorophenyl)oxazol
e,
2-(p-diethylaminostyryl)-6-diethylaminobenzothiazole,
bis(4-diethylamino-2-methylphenyl)phenylmethane,
1,1-bis(4-N,N-diethylamino-2-methylphenyl)heptane,
1,1,2,2-tetrakis(4-N,N-dimethylamino-2-methylphenyl)ethane,
N,N'-diphenyl-N,N'-bis(methylphenyl)benzidine,
N,N'-diphenyl-N,N'-bis(ethylphenyl)benzidine,
N,N'-diphenyl-N,N'-bis(propylphenyl)benzidine,
N,N'-diphenyl-N,N'-bis(butylphenyl)benzidine,
N,N'-bis(isopropylphenyl)benzidine,
N,N'-diphenyl-N,N'-bis(secondary butylphenyl)benzidine,
N,N'-diphenyl-N,N'-bis(tertiary butylphenyl)benzidine,
N,N'-diphenyl-N,N'-bis(chlorophenyl)benzidine,
triphenylamine,
poly-N-vinylcarbazole,
polyvinylpyrene,
polyvinylanthracene,
polyvinylacridine,
poly-9-vinylphenylanthracene,
pyrene formaldehyde resin, and
ethylcarbazole formaldehyde resin.
A variety of resins can be used as a resin medium for dispersing the
electron-transporting agent and the electron-generating agent. For
example, there can be used a variety of polymers like olefin polymers such
as styrene polymer, acrylic polymer, styrene-acrylic polymer,
ethylene-vinyl acetate copolymer, polypropylene, and ionomer, as well as
photocuring resins such as polyvinyl chloride, vinyl chloride-vinyl
acetate copolymer, polyester, alkyd resin, polyamide, polyurethane, epoxy
resin, polycarbonate, polyallylate, polysulfone, diallyl phthalate resin,
silicone resin, ketone resin, polyvinyl butylal resin, polyether resin,
phenol resin and epoxy acrylate resin.
These binder resins can be used in a single kind or being mixed in two or
more-kinds. Preferred resins are styrene polymer, acrylic polymer,
styrene-acrylic polymer, polyester, alkyd resin, polycarbonate and
polyallylate.
A variety of organic solvents can be used for forming the coating solution.
Examples thereof include alcohols such as methanol, ethanol, isopropanol
and butanol, aliphatic hydrocarbons such as n-hexane, octane and
cyclohexane, aromatic hydrocarbons such as benzene, toluene and xylene,
halogenated hydrocarbons such as dichloromethane, dichloroethane, carbon
tetrachloride and chlorobenzene, ethers such as dimethyl ether, diethyl
ether, tetrahydrofurane, ethylene glycol dimethyl ether, and diethylene
glycol dimethyl ether, ketones such as acetone, methyl ethyl ketone and
cyclohexanone, esters such as ethyl acetate and methyl acetate, as well as
dimethyl formamide and dimethyl sulfoxide, which can be used in a single
kind or being mixed in two or more kinds together.
Though there is no particular limitation in the composition of the
photosensitive layer, the charge-generating agent composed of the
aforementioned grains should occupy from 75 to 1% by weight and,
particularly, from 20 to 3% by weight of the whole amount on the basis of
dry weight. The charge-transporting agent, on the other hand, should be
contained in an amount of from 80 to 10% by weight and, particularly, from
80 to 30% by weight of the whole amount. When the amounts of the
charge-generating agent and the charge-transporting agent are smaller than
the above-mentioned ranges, sensitivity is not obtained to a sufficient
degree and when their amounts are larger than the above-mentioned ranges,
the charging amount tends to decrease and abrasion resistance of the
photosensitive layer tends to decrease, too.
The coating solution should have a solid component concentration of
generally from 5 to 50% by weight.
The composition for forming the photosensitive material of the present
invention may be blended with a variety of widely known blending agents
such as antioxidizing agent, radical scavenger, singlet quencher,
UV-absorbing agent, softening agent, surface-reforming agent, defoaming
agent, filler, viscosity-imparting agent, dispersion stabilizer, wax,
acceptor, and donor.
A variety of materials having electrically conducting property can be used
as an electrically conducting substrate on which the photosensitive layer
is to be provided. Examples include metals such as aluminum, copper, tin,
platinum, gold, silver, vanadium, molybdenum, chromium, cadmium, titanium,
nickel, indium, stainless steel and brass, as well as a plastic material
on which the above-mentioned metals are deposited or laminated, and a
glass covered with aluminum iodide, tin oxide or indium oxide. In general,
it is desired to use an aluminum blank tube and, particularly, a blank
tube treated with alumite such that the film thickness thereof is from 1
to 50 .mu.m.
The photosensitive layer of the single dispersion type should, generally,
have a thickness of from 5 to 100 .mu.m and, particularly, from 10 to 50
.mu.m. When the thickness is smaller than the above range, the surface
potential tends to decrease and when the thickness is larger than the
above range, on the other hand, the sensitivity decreases and the residual
potential increases.
Photosensitive Material of the Laminated Layer Type
Among the photosensitive materials of the laminated layer type of the
present invention, the photosensitive material shown in FIG. 4 has the
charge-generating layer provided on the electrically conducting substrate.
The coating composition for forming the charge-generating layer is
obtained by dispersing the charge-generating agent in the aforementioned
resin solution, and should contain the charge-generating agent in an
amount of from 99 to 1% by weight and, particularly, from 80 to 50% by
weight reckoned as solid components, and should further have a thickness
of from 0.01 to 10 .mu.m and, particularly, from 0.1 to 5 .mu.m.
Then, the charge-transporting layer is provided on the charge-generating
layer. The charge-transporting layer is obtained by dispersing the
above-mentioned charge-transporting agent in the above-mentioned resin
solution, and should contain a derivative in an amount of from 80 to 10%
by weight and, particularly, from 60 to 30% by weight per the total solid
components of the two, and should further have a thickness of from 1 to
100 .mu.m and, particularly, from 5 to 50 .mu.m.
For the positively charging applications, the charge-transporting agent in
the charge-generating agent should be chiefly comprised of an
electron-transporting agent and for the negatively charging applications,
the charge-transporting agent in the charge-generating agent should be
chiefly comprised of a positive hole-transporting agent.
Among the photosensitive materials of the laminated layer type of the
present invention, the photosensitive material shown in FIG. 8 has the
charge-transporting layer provided on the electrically conducting
substrate, and further has the charge-generating layer provided thereon.
The compositions and thicknesses of the charge-transporting layer and of
the charge-generating layer may be the same as those of the aforementioned
case.
EXAMPLES
The invention will now be explained by way of the following Examples.
In Examples, measurements were taken as described below.
Initial Properties
By using an electrostatic copy testing apparatus (EPA-8100 manufactured by
Kawaguchl Denki Co.), sheet-like photosensitive materials for
electrophotography prepared in Examples and Comparative Examples were
electrically charged by so adjusting the flow of electric current that the
initial surface potential SP1 (V) was +700 V. Then, by using an
interference filter, the lights having wavelengths of 500 nm and 700 nm
were taken out from a xenon lamp that was the source of light for
exposure, and were, respectively, projected for an exposure period of two
seconds (10 .mu.W) in order to measure their half-value exposure
quantities.
That is, the time was measured until the initial surface potential +700 V
became 1/2, and the half-value exposure quantity (.mu.J/cm.sup.2) was
found as sensitivity.
Moreover, the surface potential at a moment when three seconds have passed
from the start of exposure was found as the initial residual potential RP1
(V), and the potential attenuation factor (4) was calculated in compliance
with the following formula.
(Initial surface potential-initial residual potential)/initial surface
potential.times.100=potential attenuation factor (%)
Properties after Repetitive Use
The sheet-like photosensitive materials for electrophotography prepared in
Examples and Comparative Examples were subjected to the charging step in
which the flow of current was adjusted as described above, to the exposure
step (same as described above but without using interference filter), and
to the discharging step (irradiated with white light of 1000 lux for one
second) a hundred times repetitively using the above-mentioned
electrostatic copy testing apparatus (EPA-8100 manufactured by Kawaguchi
Denki Co.). Thereafter, the surface potential SP100 (V) and the residual
potential RP(100 (V)) were measured in the same manner as described above,
and differences from the initial surface potential and the initial
residual potential were calculated by using the following formulas.
.DELTA.SP=(SP100)-(SP1)
RP=(RP100)-(RP1)
Example 1
A perylene pigment of the following formula (4) and an X-type metal-free
phthalocyanine of the following formula (5) were pre-dispersed at a ratio
of 10 parts by weight to one part by weight in 100 parts by weight of the
THF for one hour using a ball mill, to which were then added 50 parts by
weight of an N,N-diethylamino-p-benzaldehyde diphenylhydrazone (DEH;
compound of the formula (8)) as a charge-transporting agent and 100 parts
by weight of a polycarbonate (produced by Mitsubishi Gas Kagaku Co.) as a
binder resin. The mixture was then homogeneously dispersed for one hour
using the ball mill to prepare a coating solution which was then
heat-treated at 120.degree. C. for one hour, and was applied onto an
aluminum substrate (sheet) such that the film thickness was 20 .mu.m
(grain size of aggregates: 0.2 to 2 .mu.m).
The dispersion structure in the photosensitive layer was as shown in FIG.
1.
##STR4##
Example 2
Aggregates (grain size of aggregates: 0.2 to 2 .mu.m) were formed in the
same manner as in Example 1 but using an azo pigment (compound of the
following formula (7)) instead of the perylene pigment, and a
photosensitive material was formed in the same manner as in Example 1.
##STR5##
Example 3
Aggregates (grain size of aggregates: 0.2 to 2 .mu.m) were formed in the
same manner as in Example 1 but using an a polycyclic quinone pigment
(compound of the following formula (8)) instead of the perylene pigment,
and a photosensitive material was formed in the same manner as in Example
1.
##STR6##
Example 4
Aggregates (grain size of aggregates: 0.2 to 2 .mu.m) were formed in the
same manner as in Example 1 but using an a naphthalocyanine (compound of
the following formula (9)) instead of the X-type metal-free
phthalocyanine, and a photosensitive material was formed in the same
manner as in Example 1.
##STR7##
Example 5
Aggregates (grain size of aggregates: 0.2 to 2 .mu.m) were formed in the
same manner as in Example 1 but using the perylene pigment and the X-type
metal-free phthalocyanine at a ratio of 10 parts by weight to 3 parts by
weight, and a photosensitive material was formed in the same manner as in
Example 1.
Example 6
Aggregates (grain size of aggregates: 0.2 to 2 .mu.m) were formed in the
same manner as in Example 1 but using the perylene pigment and the X-type
metal-free phthalocyanine at a ratio of 10 parts by weight to 0.2 parts by
weight, and a photosensitive material was formed in the same manner as in
Example 1.
Example 7
Aggregates (grain size of aggregates: 0.2 to 2 .mu.m) were formed in the
same manner as in Example 1 but dispersing the perylene pigment and the
X-type metal-free phthalocyanine in the THF for 100 hours using the ball
mill, and a photosensitive material was formed in the same manner as in
Example 1.
Comparative Example 1
A photosensitive material was formed in the same manner as in Example 1 but
using the perylene pigment alone in an amount of 10 parts by weight.
Comparative Example 2
A photosensitive material was formed in the same manner as in Example 1 but
using the X-type metal-free phthalocyanine alone in an amount of 1 part by
weight.
Comparative Example 3
A photosensitive material was formed in the same manner as in Example 1 but
using the X-type metal-free phthalocyanine alone in an amount of 10 parts
by weight.
Comparative Example 4
A photosensitive material was formed in the same manner as in Example i but
dispersing the perylene pigment and the X-type metal-free phthalocyanine
together with the charge-transporting agent and the binder resin without
pretreatment.
The dispersion structure of this photosensitive layer was as shown in FIG.
2, from which formation of aggregates was not recognized.
Comparative Example 5
A photosensitive material was formed in the same manner as in Example 1 but
by dispersing the perylene pigment and the X-type metal-free
phthalocyanine for 5 minutes using a ball mill as the pretreatment.
In this photosensitive material, aggregates of the metal-free
phthalocyanine have not been completely formed in the photosensitive
layer.
Comparative Example 6
A photosensitive material was formed in the same manner as in Example 1 but
using toluene for pre-treating the perylene pigment and the X-type
metal-free phthalocyanine.
No aggregates had been formed in this photosensitive layer probably because
the polarity of the solvent was so weak that no aggregate was formed.
Comparative Example 7
A photosensitive material was formed in the same manner as in Example 1 but
using benzene for pre-dispersing the perylene pigment and the X-type
metal-free phthalocyanine.
No aggregates had been formed in this photosensitive layer probably because
the polarity of the solvent was so weak that no aggregate was formed.
Comparative Example 8
A photosensitive material was formed in the same manner as in Comparative
Example 4 but using the perylene pigment and the X-type metal-free
phthalocyanine each in an amount of 10 parts by weight.
The results obtained were as tabulated below.
TABLE 1
__________________________________________________________________________
Measuring method:
Photosensitive materials were electrically charged to +700 V and
were then irradiated with monochromatic light of 10 .mu.W for 2 seconds.
SP: surface potential before exposed
RP: surface potential after exposed
Half-value Potential Charging
Property (V) after
exposure quantity
attenuation
ability
repeated 100 times
(.mu.J/cm.sup.2)
factor (%)
(.mu.A)
SP change
RP change
500 nm 700 nm 500 nm
700 nm
SP = 700 V
(.DELTA.SP)
(.DELTA.RP)
__________________________________________________________________________
Example 1
2.1 15.9 81 52 31 -10 +5
Example 2
0.6 9.3 88 60 32 -10 +6
Example 3
1.2 13.4 87 56 30 -10 +5
Example 4
2.1 16.2 81 51 30 -10 +10
Example 5
2.1 5.3 81 70 35 -16 +12
Example 6
2.1 19.8 81 50 30 -9 +12
Example 7
2.1 15.8 81 52 31 -12 +8
Comp. Example 1
2.1 was not halved
81 1 30 -11 +15
Comp. Example 2
was not halved
" 1 15 20 -- --
Comp. Example 3
" 5.0 1 73 28 -- +20
Comp. Example 4
2.1 was not halved
80 15 32 -25 +20
Comp. Example 5
2.1 " 81 16 31 -10 +8
Comp. Example 6
2.1 " 81 15 30 -10 +9
Comp. Example 7
2.1 " 81 15 30 -10 +8
Comp. Example 8
3.2 8.9 135 64 43 -120 +56
__________________________________________________________________________
Example 8
An X-type metal-free phthalocyanine and TiO.sub.2 were dispersed at a ratio
of 10 parts by weight to one part by weight in 100 parts by weight of the
THF for one hour using a ball mill, to which were then added 50 parts by
weight of the DEH as a charge-transporting agent and 100 parts by weight
of a polycarbonate (produced by Mitsubishi Gas Kagaku Co.) as a binder
resin. The mixture was then homogeneously dispersed for one hour using the
ball mill to prepare a coating solution which was then heat-treated at
120.degree. C. for one hour, and was applied onto an aluminum substrate
(sheet) such that the film thickness was 20 .mu.m.
Example 9
A photosensitive material was formed in the same manner as in Example 1 but
using TiO.sub.2 in an amount of 10 parts by weight.
Example 10
A photosensitive material was formed in the same manner as in Example 1 but
using TiO.sub.2 in an amount of 40 parts by weight.
Example 11
A photosensitive material was formed in the same manner as in Example 1 but
using SnO.sub.2 instead of TiO.sub.2.
Example 12
A photosensitive material was formed in the same manner as in Example 1 but
using antimony-doped tin oxide (SnSb.sub.x O.sub.2) instead of TiO.sub.2.
Example 13
A photosensitive material was formed in the same manner as in Example 1 but
using indium-doped tin oxide (SnIn.sub.x O.sub.2) instead of TiO.sub.2.
Comparative Example 9
A photosensitive material was formed in the same manner as in Example 8
without using X-type metal-free phthalocyanine but using TiO.sub.2 in an
amount of 50 parts by weight.
Comparative Example 10
A photosensitive material was formed in the same manner as in Example 8
without using X-type metal-free phthalocyanine but using TiO.sub.2 in an
amount of 0.1 parts by weight.
Photosensitive materials obtained in Examples 8 to 13 and in Comparative
Examples 3, 9 and 10 were evaluated for their properties and abrasion
resistance in the same manner as in Example 1. The results were as shown
in Table 2. The abrasion resistance was evaluated by measuring a
difference between the initial thickness of the photosensitive layer and
the thickness of the photosensitive layer after the copying operation was
repeated 1000 times by using a printer (LDC-630, produced by Mira Kogyo
Co.).
TABLE 2
__________________________________________________________________________
Half-value
Potential Property (V) after
Worn-out amount
exposure quantity
attenuation
Charging ability
repeated 100 times
after 10,000 times
(.mu.J/cm.sup.2)
factor (%)
(.mu.A) SP RP (.mu.m)
__________________________________________________________________________
Example 8 3.8 85 30 -10 +12 0.5
Example 9 3.1 89 33 -10 +10 0.3
Example 10 2.8 92 38 -10 +10 0.1
Example 11 3.9 85 30 -10 +10 0.5
Example 12 3.6 84 32 -10 +10 0.5
Example 13 3.6 83 32 -10 +10 0.5
Comparative Example 3
5.1 73 28 -10 +20 1.0
Comparative Example 9
-- -- not charged
Comparative Example 10
5.0 73 29 -10 +22 1.0
__________________________________________________________________________
It will be understood from the results of Table 2 that according to the
present invention, the half-value exposure quantity is small, the
potential attenuation factor is high, the residual potential difference is
small even after being treated 100 times, and the amount (.mu.m) worn out
is small even after being repeated 10,000 times. Therefore, the
photosensitive material of the present invention exhibits very high
sensitivity and excellent surface abrasion resistance.
It will be further understood that the N-type inorganic semiconductor or
photoconductor (TiO.sub.2 in Table 2) that is added in an increased amount
makes it possible to improve not only the charge generation efficiency but
also the charge-transporting efficiency and sensitivity.
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